1. Field of the Invention
The present invention relates to a technique for searching control parameters.
2. Description of the Related Art
Japanese Patent Application Publication No. 2000-35379 shows, as an internal combustion engine controller, a hardware configuration for automatically measuring performance characteristic of an engine. However, this document only shows a system configuration for automatically measuring engine performance, with which human labor can be alleviated, but the number of control parameters is enormous and the number of measurement points thus becomes large. Therefore, this configuration cannot meet a recent need for measuring engine performance characteristics in a shorter period of time.
Further, in the “CAMEO system” of AVL List GmbH (Australia), engine performance is automatically measured by the use of an experimental design method. In this system, the number of measurement points of engine performance is reduced by the experimental design method, reducing the measuring time. However, in the case of applying this to measurement of an engine which has been undergoing drastic changes with respect to control parameters, extreme reduction of the number of measurement points might make it impossible to accurately observe irregular changes in engine performance. Therefore, it is practically not possible to sufficiently reduce the number of measurement points. Moreover, since approximate positions of variation points of engine performance need be previously entered for automatic measurement, it is difficult to perform automatic measurement of an engine for which no measurement was done in the past.
Since a currently used engine has a large number of variable devices such as a universal moving valve system, a direct fuel injection system capable of injecting fuel several times in one combustion cycle, and a variable geometry supercharger, the number of command values given to those devices, namely combinations of control parameters, has become enormous.
Hence it is necessary to measure combination conditions of an enormous number of combinations of control parameters for obtaining engine performance characteristics, which is time-consuming. It is further necessary to perform measurement in various conditions in order to optimize a combination of a plurality of control parameters for each of evaluation indexes (fuel consumption, output, emission).
Accordingly, a combination of control parameters is determined in a grid shape as shown in FIG. 1 by the use of the experimental design method, and automatic measurement is performed with the control parameters automatically held at respective set values.
In a conventional automatic measurement method shown in FIG. 2, a sequence has been adopted in which, after a change in control parameter, measurement is halted until performance data is stabilized, and measurement is performed in a subsequent predetermined period of time. Hence it takes several tens of seconds to several minutes to measure performance for one measurement point (combination of control parameters). Therefore, even with the use of the experimental design method, the effect of reducing the number of measurement points (combinations of control parameters) is not sufficient, and it takes time as long as several weeks to several months to obtain engine performance in all conditions.
Moreover, the engine characteristic as described above has a highly complicated curved surface with projections and depressions relative to control parameter as shown in FIG. 3, and its changes are very abrupt. For this reason, when the number of measurement points is significantly reduced by the use of the experimental design method, it becomes impossible to catch the projections and depressions characteristics and peak points of actual engine characteristics as shown in FIG. 4. Especially when a missed peak point is the optimum value of performance that should be captured, the measurement is useless since the engine performance cannot be maximized. Accordingly, the technique based on the experimental design method that has been used in automatic measurement devices cannot practically reduce the number of measurement points and cannot shorten measuring time. In other words, when the number of measurement points is reduced, it is likely that an optimum point is missed, and that projections and depressions characteristics are missed.
Hence, in order to reduce the number of measurement points, there has been proposed a technique for searching an optimum value Pa shown in FIG. 4 by not setting a control parameter A as a condition of measurement points, and by setting the other parameters at fixed values and changing (or seeping) the parameter A only to search maximum/minimum points (hereinafter referred to as sweep method). A peak value can be searched with this technique when performance data has a single peak (MBT characteristic of ignition, etc.) as shown in FIG. 5A. However, when the performance data has a plurality of peaks as shown in FIG. 5B, searched peak value differs depending upon the sweeping direction and the starting point of the control parameter. This causes a so-called local minimum problem that has been on issue in terms of an optimization problem.
As a technique for searching such an extremum, an Extremum Seeking algorithm is known. “Real-Time Optimization by Extremum-Seeking Control” by Kartik B. Ariyur, Miroslav Krstic (Wiley-Interscience, 2003/09) is a reference book on Extremum Seeking, containing more than 200 pages.
Unfortunately, currently used automatic driving devices (AVL CAMEO) may need information about where the peak is likely to lie even in the case of single peak characteristics. No device can solve the local minimum problem.
Further, sweeping a single control-parameter is the limit in the current conditions. Sweeping a plurality of parameters has been difficult in the currently used automatic driving devices since it leads to more frequent occurrence of the local minimum problem and makes it more difficult to previously predict the position of the peak point.
In some cases, only an optimum value Pa as shown in FIG. 4 is desired to be obtained in the engine performance measurement. In such cases, in the conventional technique, engine performance is measured in a plurality of conditions as illustrated in FIG. 4, and after the measurement has been completed, an optimization process based on a plurality of pieces of measurement data is performed to ascertain the optimum value Pa. Therefore, for obtaining the optimum value Pa as quickly as possible, it is desirable to directly search the optimum value Pa, and measure performance data at the optimum value Pa.
As such, an automatic measurement device having characteristics as described below has been desired in order to obtain more sophisticated engine performance characteristics accurately and to reduce measuring time:                being capable of searching the optimum point even when the engine performance characteristic has a plurality of peaks (where a local minimum exists);        being capable of varying a plurality of control parameters to search the optimum point of the engine performance data; and        not requiring pre-data such as a place where the optimum point exists for searching the optimum point.        